Great Basin Fact Sheet No. 11: Assessing Impacts of Fire and Post-fire Mitigation on Runoff and Erosion from Rangelands
By: Frederick B. Pierson, C. Jason Williams and Peter R. Robichaud
Wildfires are a natural component of rangeland ecosystems, but fires can pose hydrologic hazards for ecological resources, infrastructure, property, and human life. This fact sheet provides an overview of the hydrologic impacts of fire on infiltration, runoff, and soil erosion. Fire primarily alters hydrology and erosion processes by consuming the protective ground cover and organic matter. The exposed bare soil becomes susceptible to increased water runoff, which detaches and transports sediment. Read on to learn the effectiveness of various mitigation treatments for reducing runoff and erosion in the years following a fire.
- Amplified runoff and erosion responses are most likely where fire increases bare ground to 50 to 60 percent and slopes exceed 15 percent. Extensive bare ground promotes accumulation of runoff and formation of high velocity concentrated flow, capable of entraining and transporting a high sediment load.
- Runoff and erosion responses are likely enhanced on steep slopes and under high rainfall intensity. Rainfall intensity and bare ground are strong predictors of post-fire responses. The hydrologic and erosion recovery period for rangelands will vary with precipitation and ground cover in the years following burning and is influenced by ecological site and pre-fire conditions.
- Risk assessment tools are available to assist in evaluation of post-fire conditions and their effects on runoff and erosion.
- Effectiveness of post-fire stabilization treatments depends on magnitude, intensity, and duration of the rainfall events following fire; ability of the treatment to increase surface cover or trap sediment; persistence of the treatment; and interaction of the treatment with vegetation and ground cover re-establishment.
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